Show flask traceback when running on production server

traceback.py

import traceback

@app.errorhandler(500)
def internal_error(exception):
    """Show traceback in the browser when running a flask app on a production server.

    By default, flask does not show any useful information when running on a production server.
    By adding this view, we output the Python traceback to the error 500 page.
    """
    trace = traceback.format_exc()
    return("<pre>" + trace + "</pre>"), 500

Doesn't work.

Confirmed, doesn't work here either